Recent years have seen an increase in the number of applications for video on demand type services, such as video-conferencing through the Internet, digital video broadcasting, and streaming video content. These applications depend on transmission of video information. These applications require that such video data having a substantial amount of digital data is transmitted through conventional transmission channels having limited bandwidth or recorded on conventional recording media having limited data capacity. Accordingly, in order to transmit the video data using a conventional transmission channel or record the video data onto a conventional recording medium, compression or reduction of the amount of the video data is necessary.
Many video coding standards have been developed for the purpose of compressing video data. In conventional image coding methods represented by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) standards denoted as H.26x and the ISO/IEC standards denoted as MPEG-x, the screen is divided into predetermined units, and coding is performed on these units. For example, with H.264/MPEG-4 AVC (for example, see Non Patent Literature 1), the screen (picture) is processed in units called macro blocks, each of which constitutes a 16 by 16 pixel block.
In the coding and decoding processes, each of the plurality of processing units, macroblocks, are processed in order from the processing unit on the left side of the screen to the processing unit on the right side. It is to be noted that when each macroblock is further divided into smaller units called blocks, processing is performed on each block in a z-pattern, zigzag order.
In addition, in the High Efficiency Video Coding (HEVC) that is considered to be the next-generation image coding standard (see Non Patent Literature 2, for example), processing in units of mutually different sizes, from units of even larger blocks (64 by 64 pixels) to units of smaller blocks (8 by 8 pixels), is possible.